The present invention is directed to systems for supplying ink to the print heads of ink-jet printer pens.
Pens used with ink-jet printers include print heads that eject minute droplets of ink through nozzles. An ink supply reservoir is associated with the pen. Certain print heads, known as drop-on-demand type, employ thermal or piezoelectric mechanisms that are responsive to control signals for expanding or compressing, respectively, small volumes of ink near each print head nozzle to eject drops therefrom onto print media.
The ink supplied from the pen reservoir flows in a single path toward the print head and out a nozzle. When nozzles are not ejecting drops, there is substantially no flow of supply ink in the vicinity of the nozzle. When the printer is activated but between printing operations, the flow of supply ink is generally still with respect to the entire print head.
The present invention is directed to ink circulation in ink-jet pens, and particularly to a system for supplying ink to a print head in such a manner that the ink circulates with respect to the print head nozzles while the printer is activated, irrespective of whether the print head is simultaneously operating to eject ink drops.
The present invention may be embodied in a pen employing a single print head, or in a pen that employs several print heads.
The circulation system provides numerous advantages to the printing operation. For example, ink circulation facilitates the removal of air from ink. In this regard, air tends to diffuse into the ink supply, especially when the fluid pressure of the supply is maintained slightly below ambient, as is required with many ink-jet pen designs for the purpose of avoiding leakage of ink through inactive nozzles.
The ink circulation system is also effective for dissipating heat that may be generated by the print head. In instances where more than one print head is employed, the circulation system across all print heads tends to evenly distribute the heat so that the entire array of print heads operate at substantially the same temperature.
In accordance with another aspect of this invention, the heat-dissipation effects mentioned above may be regulated by the incorporation of a heat exchanger for promoting even heat distribution and for maintaining a constant, optimum, operating temperature for the print head.
The ink circulation system, when employed with pens using color inks, helps to prevent changes in the relative concentrations of dye and solvents that may otherwise occur in systems where non-circulating ink is present.